They’ve met to do their unscripted podcast, Brain Coffee. Today’s topic is the midlife crisis, which, granted, isn’t hitting these two too hard. Mainly, they’re trying to figure out how to make even more of a difference, expand their impact on medicine.

Other guys buy chili-pepper-red sportscars; women have quiet affairs or find themselves a guru. People obsess over new causes or hobbies, desperate for some dramatic change that will jack up the excitement.

Meanwhile, what’s going on beneath our conscious awareness is that our brains are becoming less plastic, less able to learn and change and adapt. We have a happy little protein called BDNF (brain-derived neurotrophic factor) that allows our neurons to regenerate and their synapses to make and break and alter connections, reorganizing as we learn. But as we hit midlife, our BDNF levels have peaked and started to drop. And as Leuthardt points out, “reduced plasticity is associated with depression. So there’s this perfect storm: Just when you’ve reached all your initial life goals and you’re trying to figure out your next phase, your brain stops cooperating.”

What can you do to keep your BDNF level high? Above all, exercise. Some studies say strength training; others say aerobic; still others say a combination of the two. But there’s a general agreement that physical exercise keeps the brain supple—as does cognitive exercise.

“If you’re a lifelong learner, constantly engaged with people, reading books, taking on new tasks, you do better than someone whose brain is not engaged, and whose life is more regimented,” Leuthardt tells me after the podcast. (It also helps if you’re healthy—not obese, not smoking or drinking to excess, not diabetic.)

Still, midlife is an understandable time for a crisis. “Your brain plays a big role in where you are in the world,” Leuthardt says, “and sometimes you don’t have full control over what it does.” The convergence of genes (BDNF) and environment (the early goals accomplished, or failed, and now what?) has to get resolved somehow.

On the podcast, Leuthardt brings up the benefits of simply taking a walk, which often eases depression.

“That’s gonna solve what the girlfriend and the Ferrari are for?” Kim teases.

What’s so magical about walking, I ask later. “It’s good physical exercise,” he says, “but at the same time—and this is just me speculating—you’re not taxing your body with a long marathon, elevating cortisol and stressing your joints.” So, for once, it’s gain without the pain. Also, you’re moving through space, which contradicts that feeling of stuckness. “Walking in green spaces has a meaningful impact on depression. Increasingly we’re learning that depression is a network imbalance.”

A what?

Leuthardt explains that the brain has competing networks of attention, some of them focused on the outside world and some intrinsic. One of the big players in the intrinsic network is called the default mode network, in which we’re introspective, maybe daydreaming or ruminating, self-aware but not goal-oriented. It comes to the fore when we’re depressed, pushing aside the extrinsic network, which is visual and sensory, all about motor skills and goal-oriented behavior and our quest for meaning and purpose.

Walking is a goal-oriented and purposeful act, and it reconnects us to our senses and to the external world, restoring the balance in our attention.

The change we crave at midlife might also be a way to restore balance, Leuthardt says, and get a little more plasticity back in our brain. We’re not learning and adapting as readily, and we’re getting depressed about it. “So you force a change,” he says, “and that forces your brain to change, which requires elevated BDNF.” It’s a great plan if it works. But if you can’t muster enough BDNF to pull it off, “you’re left with higher stress and an inability to cope. It’s like going off the diving board when you can’t swim: You’ll either sink or learn how to swim.”

“Novelty is a cheap substitute,” Leuthardt retorts. “If you find a new goal, a new meaning, it rebalances those networks. You are less focused on yourself. The Ferrari and the new girlfriend are transient pleasures, but they don’t rebalance the network.”

On the Brain Coffee podcast, Dr. Eric Leuthardt and Dr. Albert Kim talk about health, technology, and the many ways neuroscience affects our behavior. In 2019, they'll stage BrainWorks, a performance about advances in neuroscience that takes place in an intimate theater setting. The idea? For listeners or audience members to lean back, relax, and open up their minds.